Left hemisphere dominance for language in young adults: a High-Density EEG protocol validation (CATCH IN HEAD project)

The left hemisphere is generally recognized as the dominant side for language in the general population; differences in brain lateralization for language have also been proven to be important in psychoses and in auditory hallucinations in normal adults. This validation study aimed to determine the most effective task for exploring language lateralization by visualizing electroencephalography (EEG) component dynamics and mapping the associated brain regions in a population of healthy young adults. Our goal was to develop a solid protocol to assess lateralization to further expand our study to the investigation of the full spectrum of auditory manifestations both in normal and in pathological subject groups. We collected data of n=30 participants, all healthy, right-handed adults (15F/15M, mean age=23 ± 2.3) that were all Italian native speakers. Participants performed two computerized linguistic tasks (Rhyme Judgment and Verb Generation), while the EEG activity was recorded with a 256-channel High-Density EEG. We mapped the spatial localization of electrodes by means of 3D scanning. After preprocessing the data, we created a head model for every subject by using their individual structural magnetic resonance images, and then performed analyses of the ERP components and neural generators. For behavioral data, we analyzed mean accuracy and reaction time. Source analysis showed that Rhyme Judgment determined greater left hemisphere lateralization for both early (200, 375, 750 ms) and late (CNV) ERPs, while Verb Generation showed a more distributed activation pattern involving the right hemisphere. Performances in both tasks were optimal (>95% of accuracy, <1000 ms of reaction time). These findings suggest that the Rhyme Judgment is a valuable approach to elicit the left hemispheric lateralization for language. This validated protocol provides a solid foundation for future investigations into auditory hallucinations across both healthy and clinical populations, where linguistic hemispheric dominance is expected to be altered.